This invention relates in general to pressure-sensitive adhesives and in particular to repulpable tapes which retain adhesion and tack over a wide range of humidity and temperature.
Since the need for repulpable tapes is widely recognized in our waste conscious, efficiency conscious and natural resource preservation conscious society, efforts have been made to produce such a product. Illustrative of such attempts are U.S. Pat. No. 4,569,960; 4,413,080 and 3,865,770 all issued to Blake; U.S. Pat. No. 3,441,430 issued to Peterson; U.S. Pat. No. 4,442,258 issued to Sunakawa; and U.S. Pat. No. 4,482,675 issued to Witt and invented by the present assignee.
While the aforementioned tapes are all successfully water-dispersible they vary in repulpability, tack and shear strength (also referred to as creep) and all three properties are not optimally met over a wide range of relative humidity. Shear strength and relative humidity stability are advantageous properties given the commercial application of repulpable tapes, namely the paper industry.
Any industry which uses or makes rolls of paper, requires a continuous operation and consequently requires tape which allows for the uninterrupted feeding of one roll of paper to another.
These properties are particularly advantageous in the paper making and printing facilities wherein repulpable splicing tape is necessitated to connect the beginning of one roll to the end of another to assure continuity or to reconnect cut-out defective segments.
Continuity is further advanced by the repulpable property of such tapes in that the repulpability eliminates separating the tape from the paper waste. Moreover, since the tape is recyclable it is also ecologically advantageous because the tape can be thrown in with the paper waste. However, the largest promotor of continuity is adhesion.
The physical conditions that exist in the paper manufacturing facilities are variable ranging from hot to cold temperature and low to high relative humidity given the amount, length or speed of production. Thus, it is highly desirable for an efficient and continuous operation to have tapes that are stable i.e., maintain adhesion over a wide range of physical extremes such as low and high relative humidity. Although the prior art teaches water-dispersibility it does not teach how to achieve repulpability, tack and creep simultaneously over a wide range of relative humidity. These shortcomings are evident in the aforementioned illustrative patents, which will now be described in detail.
U.S. Pat. No. 3,441,430 issued to Peterson describes repulpable splicing tapes which adhere to wet or hydrophilic surfaces which are made by coating one or both surfaces of a paper backing with a water-soluble copolymer of an acrylic acid and an ether acrylate, plasticized with at least an equal amount of a liquid water-soluble plasticizer having at least one ether linkage, e.g., polyethylene glycol monophenyl ether. Due to the ether linkage and resultant oxidation sensitivity it loses significant tackiness, flexibility, and repulpability when exposed to high temperature and humidity.
U.S. Pat. No. 3,865,770 issued to Blake describes water-soluble acrylate vinyl carboxylic acid copolymers partially neutralized with alkanolamines.
U.S. Pat. No. 4,413,080 issued again to Blake describes a water-dispersible pressure-sensitive adhesive wherein certain acrylate:acrylic acid copolymers are blended with acidic rosin or rosin derivative, partially neutralized with KOH in combination with NaOH and/or LiOH, and plasticized with an oily water-soluble polyoxyethylene compound.
U.S. Pat. No. 4,569,960 issued to Blake describes a blend of acrylate:acrylic acid copolymer, NaOH and/or LiOH, KOH, and certain ethoxylated plasticizing components. This patent is an improvement over the previous U.S. Pat. No. 4,413,080 issued to Blake in that it describes the disadvantages of the previous patent as follows: "upon exposure to elevated temperatures, the plasticizer may separate and migrate into layers of paper adjacent the splice, causing transparentization and decreased adhesion" Column 2, line 25-29. Notably, Pat. No. 4,413,080 and 4,569,960 primarily address splicing carbonless paper without adversely affecting its performance, whereas U.S. Pat. No. 3,865,770 addresses splicing tapes in general.
In sum, while the tapes described in the aforementioned Blake patents maintain tack in a low humidity environment i.e. below 20%, they lose significant tack in a high humidity environment i.e. above 85%.
U.S. Pat. No. 4,442,258 issued to Sunakawa et. al. describes a "polymerization product obtained by the solution polymerization of a water-soluble ethylenically unsaturated monomer, alone or in combination with a water-soluble ethylenically unsaturated monomer copolymerizable with the water-soluble ethylenically unsaturated monomer, in the presence of a plasticizer selected from the group consisting of polyetherpolyols and polyhydric alcohols having a molecular weight of less than 3,000 and which is liquid at room temperature." Column 2 Lines 55-64. While this product is repulpable and maintains good tack over a broad range of humidity, it gives variable creep at 150.degree. F. (2-100 hr) and at 70.degree. F. (approximately 8 hrs).
Lastly, U.S. Pat. No. 4,482,675 issued to Witt and invented by the present assignee describes a composition comprising acrylate based polymer systems containing carboxylic functionality which are at least partially esterified with an ethoxylate of alkyl phenol or aliphatic alcohol and then at least partially neutralized with alkaline material. While the Witt paper splicing tape is water soluble and repulpable, its adhesive properties are water dependent. Hence, as the percent of moisture increases, the tack increases. Consequently, under low moisture environmental conditions, misting is required. The present invention maintains repulpability plus it advantageously alleviates the need for misting while simultaneously improving tack and shear strength, i.e. adhesion.